Electrical insulation



Patented Feb. '11, 1941 UNITED STATES 2.231.595 ELECTRICAL msom'rron Moyer M. Saflord, Roy

0. Feagin, and Birger W.

Nordlandcr, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York No Drawing. Application August 31, 1938, Serial N 227,750

Claims.

The present invention relates to electrical insulation and particularly to improved electrical insulation compositions which contain plasticized polyvinyl halides.

Plasticized polyvinyl halide compositions, such as those described and claimed in Semon Patent 1,929,453 of Oct. 10, 1933, are synthetic rubber-like compositions. For example, gamma polyvinyl chloride plasticized with tricresyl phosm phate yields a composition which is rubber-like in character but is not as susceptible to chemical attack as is rubber. These compositions are,

however, electrically poor in character since they exhibit high power factor and high dielectric losses, particularly at higher voltages and high temperatures.

In accordance with the present invention, it has been discovered that a lead salt of a phenol markedly improves the electrical properties and electrical stability of plasticized polyvinyl halides.

One example of the invention is an electrical insulation composition comprising polyvinyl halide, tricresyl phosphate and the lead salt of p-tertiary amyl phenol. ample, that a composition containing 60% by weight of polyvinyl chloride and 40% by weight of tricresyl phosphate, which-exhibits a power factor at 90 C. and 60 cycles of 98% and a loss factor (6) of the order of 4500, is so improved by the addition of as little as 3% of the lead salt I of p-tertiary amyl phenol, that the power factor at 90 C. and 60 cycles is 0.084 and the loss factor is 0.780.

Another example of the invention is an electrical insulation composition containing polyvinyl chloride, tricresyl phosphate and basic lead phenolate. Such a composition containing 2% weight of the lead phenolate shows a power factor at 90 C. and 60 cycles of 0.121 and a loss factor of 1.17.

In carrying the invention into practice it is imortant properly to incorporate the class of compounds in question with the plasticized polyvinyl halide composition. The ingredients preferably,

are compounded by milling on differential rollers such as are used in standard rubber com- It was found, for ex- 7 pounding practice, but it is important that the rolls be set at the proper distance from each other and that the temperature and time of milling be carefully controlled. The setting of the rollers must be determined from their size and the temperature and time of milling is dependent on the size of the batch being compounded. For example, using a. 100 gram batch of a composition containing Per cent Polyvinyl chloride 57.5 Tricresyl phosphate 40. Lead salt of p-tertiary amyl phenol in which the lead salt was first incorporated in the tricres'yl phosphate at room temperature and the solution thoroughly dispersed into the dry polyvinyl chloride, it was found that the optimum results on a 6-inch diameter laboratory mill in which the rolls were travelling at 32 R. P. M. were obtained when the rolls were set approximately 3 to 10 mils apart and a temperature of 126 to 132 C. was used. There was a very decided lowering of the electrical losses for the ther milling produced only slightly lower electrical losses.

-An advantageous addition is a finely divided carbon black such as the carbon black known to the trade as Dixie Special #102. The use of a small percentage, say about 2% of the finely divided carbon black, with the compositions of the present invention produces'a still further lowering of the electrical losses.

Ageing of the compositions of the invention at elevated temperature for a period of time also has a beneficial effect in handling large factory batches. For example the dielectric losses can be considerably reduced by allowing the compositions to age in an air oven at 125 C. several hours.

The following table shows illustrotively ex amples of some of the various compounds which may he used in carrying out the invention to gather with electrical data on power factor and loss factor (6') as compared to a compost tion containing 60% polyvinyl chloride and 40% tricresyi phosphate:

first 20 to 30 minutes of milling after which fur- Percent Power Percent Percent Lo polyvinyl g gg Lead salt oicarbon ,figig not: m] chloride phosphate) black 69 We is") a 38 T... H. w psryam eno 3 0. 58 i0 fl-Na hthohni 2 a? 58 to Tort ryamyl fl-naphthol..- 2 2.46 5 58 40 p-Phenyl phenol 2 1.37 58 40 o-Phcnyl phenol 2 1.10 56.5 40 0. 150 58 40 1.17 58 it) 4.22 58 40 1.17 54.6 40 0.576 00 It is to be understood that the compounds, proportionsand figures given are illustrative of the invention but not limiting in character. Ihe

term a lead'salt of a phenol as used in the claims is intended to embrace the lead salts of the higher phenols such as the naphthols and.

3. Electrical insulation-.havinglow power factor and low electrical loss factor comprising gamma polyvinyl chloride, tricresyl phosphate and a lead salt of a phenol.

4. Electrical insulation having low power factory and low electrical loss factor comprising plasticized gamma polyvinyl chloride, a lead salt of a phenol, and a finely divided carbon black.

5. Electrical insulation having low power factor and low electrical loss factor comprising gamma polyvinyl halide, plasticizer and a lead salt of a phenol.

MOYER M. SAFFORD. ROY C. FEAGIN. BIRGER W. NORDLANDER. 

